The present invention relates to utilizing an electromagnetic assembly to securely clamp a structure, such as a multiple layer structure, and in particular to securely clamp the structure at a location where an operation is to be performed on the structure, while not obstructing the location where the operation is to be performed.
In many industries, operations must be performed on structures, such as multiple layer structures, and problems arise if the multiple layers of the structure cannot be securely held together during the operation. For example multiple layer structures, particularly those structures that are subject to significant dynamic forces and/or pressure over their lifetime, such as aircraft bodies, bridges, vehicle bodies, buildings, and others, must be properly secured with fasteners and/or adhesive in order to ensure that the structure will perform as intended over its lifetime.
Typically, to properly secure a fastener in a multiple layer structure, a hole must be drilled through the multiple layer structure at the desired location of the fastener. The hole must not have any sharp edges, i.e., burrs, there must not be debris between the layers, and any sealant applied between the layers in order to make the structure air and/or water tight must be sufficiently squeezed out. When excess sealant is present between the layers, the distance between the layers is increased and/or uneven, which may be referred to as a “gasket” condition. Thus, if burrs, debris and/or excessive sealant are present, then the layers cannot be properly fastened, and the layers may suffer corrosion, cracking and/or premature fatigue failure, which generally renders the structure ineffective for its intended purpose and, therefore, subject to the expense of repair or replacement.
Ensuring that a proper hole is drilled is, therefore, an integral part of fastening multiple layer structures together. In the aerospace industry, for example, a significant amount of time and labor is expended ensuring that the holes through the various layers of the aircraft structure are appropriately drilled, cleaned, sealed and fastened. Initially, the layers of materials that form the structure are loosely assembled without sealant, and drill templates are aligned and attached to the structure in the areas to be drilled. A drill operator, guided by the drill template, then drills holes through the layers of materials typically using a manual drill motor. As the hole is being drilled through the layers, the drill bit tip pushes with the full feed force applied to the drill motor. This can cause a gap to develop between a drilled layer and the next layer, particularly when the layers are a stack-up of thin material. The gap between the layers causes burrs about the hole and debris is likely to gather between the layers. Thus, once the holes are drilled, the layers must be disassembled, the burrs must be removed from the holes, and the debris must be cleaned from the surfaces of the layers, all of which is a time-consuming and labor intensive process.
Sealant is then applied to the layers prior to re-assembling the layers. In order to ensure the layers are properly sealed to provide an air and water-tight seal, a generous amount of sealant is applied to the layers. Clamps that extend through the holes, such as KWIK-LOK™ clamps commercially available from Zephyr Manufacturing Company, Inglewood, Calif., must be placed through each hole of the reassembled layers in order to squeeze out the sealant to prevent excessive “gasket” between the layers before the sealant dries. The extra sealant squeezes out around the clamps and must be cleaned from the structure and the clamps during clamping and/or after the clamps are removed. If the holes are satisfactory, then fasteners may be installed and fastened with nuts or swage lock collars. Overall, this process is expensive, laborious, and time-consuming. In addition, the integrity of the resulting holes depends upon the completion of many manual processes, which creates a risk that certain steps may be performed inadequately or completely overlooked.
In addition, when adhesive is utilized to bond multiple layers of a structure, then the layers typically must be clamped together as the adhesive cures or dries to ensure that the adhesive is sufficiently spread between the layers and that the spacing between the layers is minimal. Thus, conventional clamps, such as C-clamps are utilized to hold the layers together as the adhesive cures or dries. Various sizes of the clamps may be used for various sizes of structures. For instance, for relatively large structures, C-frame tools may be used. The clamps, however, require that at least a portion of the structure is accessible from at least one side for the arms of the clamp to reach around. For complex structures and structures that are not easily accessible, it is difficult if not impossible to utilize a clamp. In addition, bulkheads, fittings and the like in the structure also interfere with the use of a clamp on the structure.
Many of the tasks detailed above could be avoided if a technique existed for clamping multiple layer structures together securely enough to prevent the layers from separating during an operation. In particular, a need exists for a clamping technique that securely holds the multiple layers of a structure together proximate the location where the operation is to take place. The needed technique should therefore provide a way to perform operations on a multiple layer structure that is more efficient, faster and less expensive than the conventional procedures utilized in performing such operations.
Conventional electromagnets have been considered to clamp multiple layer structures together, such as by positioning an electromagnet on one side of the structure and a piece of ferrous material on the other side. If any gap exists between a conventional electromagnet and the ferrous material, however, significant losses in the force between the electromagnet and the ferrous material result. Conventional electromagnets, therefore, do not create enough force to securely clamp multiple layers of a structure together because the force between a conventional electromagnet and the piece of ferrous material is subject to the inverse square law, i.e., the force is proportional to the inverse square of the distance between the electromagnet and the piece of ferrous material. For example, a conventional electromagnet, such as the EM-476 flat-faced electromagnet commercially available from Magnetool, Inc. of Troy, Mich., with dimensions of 4″×8″×2½″ creates a force of 2000 lbs. on a piece of ferrous material when no gap exists between the electromagnet and the ferrous material. If a 1/16-inch gap of air or any non-ferrous material is introduced between the electromagnet and the ferrous material, the force between the electromagnet and the ferrous material drops to 95 lbs., which is not a sufficient amount of force to securely clamp a multiple layer structure together. Since the structures are often formed of a non-ferrous material, however, this marked decrease in the clamping force due to the gap created by the structure poses a significant limitation upon the use of electromagnets for clamping any type of structure, including multiple layer structures.
Therefore, to utilize an electromagnet for clamping a multiple layer structure, an electromagnet capable of creating a significant amount of force between the electromagnet and a piece of ferrous material, even when there is a gap between the electromagnet and ferrous material, is needed. In particular, the needed electromagnet must create a sufficient amount of force to securely clamp multiple layer structures such that an operation, such as drilling, may be performed on the structure.